opentelemetry-java-instrumentation/instrumentation/runtime-telemetry-jfr/library

The main entry point is the JfrTelemetry class in the package io.opentelemetry.instrumentation.runtimetelemetryjfr:

// Initialize JfrTelemetry
JfrTelemetry jfrTelemetry = JfrTelemetry.create(openTelemetry);

// Close JfrTelemetry to stop listening for JFR events
jfrTelemetry.close();

JfrTelemetry works by subscribing to certain JFR events, and using relevant bits of information from the events to produce telemetry data like metrics. The code is divided into "handlers", which listen for specific events and produce relevant telemetry. The handlers are organized into features (i.e JfrFeature), which represent a category of telemetry and can be toggled on and off. JfrTelemetry evaluates which features are enabled, and only listens for the events required by the handlers associated with those features.

Enable or disable a feature as follows:

JfrTelemetry jfrTelemetry = JfrTelemetry.builder(openTelemetry)
  .enableFeature(JfrFeature.BUFFER_METRICS)
  .disableFeature(JfrFeature.LOCK_METRICS)
  .build();

The following table describes the set of JfrFeatures available, whether each is enabled by default, and the telemetry each produces:

JfrFeature	Default Enabled	Metrics
BUFFER_METRICS	false	process.runtime.jvm.buffer.count, process.runtime.jvm.buffer.limit, process.runtime.jvm.buffer.usage
CLASS_LOAD_METRICS	false	process.runtime.jvm.classes.current_loaded, process.runtime.jvm.classes.loaded, process.runtime.jvm.classes.unloaded
CONTEXT_SWITCH_METRICS	true	process.runtime.jvm.cpu.context_switch
CPU_COUNT_METRICS	true	process.runtime.jvm.cpu.limit
CPU_UTILIZATION_METRICS	false	process.runtime.jvm.cpu.utilization, process.runtime.jvm.system.cpu.utilization
GC_DURATION_METRICS	false	process.runtime.jvm.gc.duration
LOCK_METRICS	true	process.runtime.jvm.cpu.longlock
MEMORY_ALLOCATION_METRICS	true	process.runtime.jvm.memory.allocation
MEMORY_POOL_METRICS	false	process.runtime.jvm.memory.committed, process.runtime.jvm.memory.init, process.runtime.jvm.memory.limit, process.runtime.jvm.memory.usage, process.runtime.jvm.memory.usage_after_last_gc
NETWORK_IO_METRICS	true	process.runtime.jvm.network.io, process.runtime.jvm.network.time
THREAD_METRICS	false	process.runtime.jvm.threads.count